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    <title>ShellCheck: SC2143 – Use `grep -q` instead of comparing output with `[ -n .. ]`.</title>
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    <h1>SC2143 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC2143">See this page on GitHub</a>
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    <h2 id="use-grep--q-instead-of-comparing-output-with---n--">Use
<code>grep -q</code> instead of comparing output with
<code>[ -n .. ]</code>.</h2>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC2143.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">[</span> <span class="st">&quot;</span><span class="va">$(</span><span class="fu">find</span> . <span class="kw">|</span> <span class="fu">grep</span> <span class="st">&#39;IMG[0-9]&#39;</span><span class="va">)</span><span class="st">&quot;</span> <span class="bu">]</span></span>
<span id="cb1-2"><a href="SC2143.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="cf">then</span></span>
<span id="cb1-3"><a href="SC2143.html#cb1-3" aria-hidden="true" tabindex="-1"></a>  <span class="bu">echo</span> <span class="st">&quot;Images found&quot;</span></span>
<span id="cb1-4"><a href="SC2143.html#cb1-4" aria-hidden="true" tabindex="-1"></a><span class="cf">fi</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC2143.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="fu">find</span> . <span class="kw">|</span> <span class="fu">grep</span> <span class="at">-q</span> <span class="st">&#39;IMG[0-9]&#39;</span></span>
<span id="cb2-2"><a href="SC2143.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="cf">then</span></span>
<span id="cb2-3"><a href="SC2143.html#cb2-3" aria-hidden="true" tabindex="-1"></a>  <span class="bu">echo</span> <span class="st">&quot;Images found&quot;</span></span>
<span id="cb2-4"><a href="SC2143.html#cb2-4" aria-hidden="true" tabindex="-1"></a><span class="cf">fi</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>The problematic code has to iterate the entire directory and read all
matching lines into memory before making a decision.</p>
<p>The correct code is cleaner and stops at the first matching line,
avoiding both iterating the rest of the directory and reading data into
memory.</p>
<h3 id="exceptions">Exceptions</h3>
<p>The <code>pipefail</code> bash option may interfere with this
rewrite, since the <code>if</code> will now in effect be evaluating the
statuses of all commands instead of just the last one. Be careful using
them together.</p>
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